1. Field of Invention
The invention relates to an ultrasonic motor used in the precision opto-electrical manufacturing industry, and more particularly, to an piezoelectric ultrasonic motor with multi-layer thin disks that can produce homogeneous forward and reverse driving forces.
2. Related Art
To improve human life, many scientists and inventors produced many convenient devices and mechanisms. In particular, the introduction of the electromagnetic motor had brought great progress to the world. It had been invented more than one hundred years ago. Since then, the electromagnetic motors had been widely used in machine-related manufacturing industries. However, aside from new discoveries in superconductors and magnetic materials, there is not much progress in motors. It is very hard for either conventional motors or small motors with sizes less than 1 cm to overcome the problem of power conversion rate. Therefore, a new motor driven by high power ultrasonic wave energy has received a lot of attention by the public. We call this kind of motor the ultrasonic motor.
Although this type of motors has a different mechanical structure, it is still based upon the same theory, which was proposed by V. V. Lavrinekon and P. E. Vasilievthe in the former Soviet Union. Due to the unstable structure, is had not been widely used until 1980s. After the semiconductor industry arose, a motor that is free from electromagnetic interference (EMI) and also capable of performing precision controls is needed. Such an urgent need accelerated the development of ultrasonic motors. In fact, the first ultrasonic motor was introduced by H.V. Barth at IBM in 1973, starting the new era of ultrasonic motors. In the past decade, the manufacturing technique for ultrasonic motors had tremendous progress. which is particularly true in Japan.
The ultrasonic motor uses the elastic vibrations produced by ultrasonic waves (with a frequency above 20 kHz) to obtain the driving force. Such a driving force brings the rotor into motion by friction. An alternate voltage as a driving source is supplied to a piezoelectric ceramic to produce alternate expanding and shrinking motions. Although the expanding and shrinking scale is only a few micrometers (xcexcm), the frequency is hundreds of thousand times per second and thus the piezoelectric ceramic can move several centimeters per second. This is ideal for related scientific products.
Although this type of ultrasonic motors has the advantages of being quiet, efficient, small and light, it has the problem of abrasion. Moreover, the forward and reverse driving forces are different, resulting in a big difference in the output power. Thus, there are great troubles in practical uses.
In view of the foregoing, the invention provides a piezoelectric ultrasonic motor with multi-layer thin disks. Several sets of symmetric buzzer disks are employed to produce expanding and shrinking deformations to transport kinetic energy to the exterior. Therefore, not only can homogeneous forward and reverse driving forces be provided, the driving ability and elasticity of the whole system are largely enhanced while the abrasion is reduced.
The disclosed piezoelectric ultrasonic motor with multi-layer thin disks mainly includes several sets of driving modules. The driving module contains two symmetric buzzers, which of which consisting of a buzzer disk and a connected elastic vibration disk. The buzzer disk is made of a piezoelectric ceramic, and the elastic vibration disk is a metal. The buzzer disk is installed with three fixing elements. When the buzzer disk is supplied with an alternate voltage, it undergoes alternate expanding and shrinking deformations. Through the fixing elements, the elastic vibration disk generates mechanical waves that propagate along the radial and arc directions. A standing wave thus forms on the edge of the elastic vibration disk. Although the deformation is only several micrometers in scale, the driven object can be moved by several centimeters as the deformation frequency is tens of thousand times per second. The motor provides a highly precise driving force. By controlling the frequency of the alternate voltage, different motion speeds can be provided to the external object. Moreover, the boundary conditions of the buzzer disks in the two buzzers of the driving module are opposite so that the driving force is in unison. Therefore, when supplying the buzzer an alternate voltage for a forward driving force, the other symmetric buzzer is supplied with an auxiliary alternate voltage so that they both provide forward driving forces together. When one needs a reverse driving force, all he or she needs to do is to reverse the alternate voltage input. Consequently, the same driving force is provided no matter it is forward or reverse in direction.
The disclosed ultrasonic motor utilizes several sets of driving module consisted of two buzzers with opposite boundary conditions to provide a high driving force that is smooth in both forward and reverse directions. Since the driving modules are connected in series, the contact area between the driving modules and the external driven object increases. The area of each individual part can be made smaller, minimizing the size of the whole module without sacrificing the output driving force. Moreover, modifying the arrangement of the driving modules can produce different functions for various applications. Therefore, the invention can solve the problem of a big difference in the forward and reverse driving forces as in the prior art. It greatly increases the stability and elasticity of the system, rendering a smoother motion with less friction.